The present invention relates generally to AC line stabilization circuitry for high power factor loads. More specifically, the invention provides AC line stabilization circuitry for protection of bulkless AC/DC converters from failure caused by lightning or other energy surges applied to the line, while simultaneously providing additional holdover capacity for line drop-out conditions.
Conventional bulkless converters do not include large electrolytic capacitors to absorb lightning and other energy surges applied to electrical lines. As a result, high peak input capacitor voltages applied to an AC/DC converter may result in a failure. Moreover, bulkless converters known to the art require, large capacitors at the output of the converters to provide sufficient holdover as the AC line voltage drops out. It is the primary object of the present invention to provide stabilization circuitry for bulkless converters to more efficiently absorb lightning and energy surges to prevent capacitor voltage applied to the input of the converter to rise to unacceptably high peaks. It is a further object of the invention that said stabilization circuitry further provide a holdover during AC line voltage drop-out utilizing a smaller electrolytic capacitor than heretofore known to the art. Other objects and advantages of the present invention will become apparent to those skilled in the art.
It is noted that AC line stabilization circuits for providing a wide range of circuit stabilization features are generally well known to the art. Such known circuitry includes, for example, surge protection circuits, voltage suppression circuits and circuit breakers (for both high and low power factor loads) to protect circuitry coupled to a AC line during power-up conditions, to provide protection from lightning and other energy surges applied to the line; and circuits for providing supplementary hold-up time capacity to drive a given load in the event of power outages in the AC line.
Specific examples of the aforementioned circuitry representing the current state of the prior art, include U.S. Pat. No. 4,091,434, issued on May 23, 1978 to Suzuki et al for a surge current protection circuit; U.S. Pat. No. 4,573,113 issued on Feb. 25, 1986 to Bauman for a surge protection system for a DC power supply during power-up; U.S. Pat. No. 4,837,672, issued on Jun. 6, 1989 to Donze disclosing an electronic switched power supply for automatically adjusting the operation thereof to produce a fixed output voltage as input voltages of different magnitudes are applied thereto at different times; U.S. Pat. No. 4,811,189, issued on Mar. 7, 1989 to Harvest et al, which discloses an AC rectifier circuit with means for limiting the rectified voltage; U.S. Pat. No. 4,524,413, issued on Jun. 18, 1985 to Ikenoue et al, for an AC rectifier having a semi-conductor active rectifying element; U.S. Pat. No. 4,412,278, issued on Oct. 25, 1983 to Cambier, et al, for a AC to DC converter using polarized input isolation capacitors; and U.S. Pat. No. 4,327,405, issued on Apr. 27, 1982 to Clark, Jr., disclosing a voltage suppression circuit for a DC to DC voltage converter circuit.
None of the aforementioned prior art references discloses or suggests the AC line voltage stabilization circuitry in accordance with the present invention. Briefly stated, the Harvest et al patent does not disclose a power factor correction circuit; the Ikenoue et al patent provides an AC rectifier circuit with an overvoltage protection circuit which shuts the circuit down; the Donze patent discloses a switched mode power supply with output voltage control, but does not provide power factor correction; the Clark, Jr. patent discloses a voltage suppression circuit responsive to voltage polarity reversal in a transformer primary, and thus is not directly relevant to the invention disclosed and claimed herein; the Cambier et al patent discloses an AC to DC converter using polarized input isolation capacitors which is not directly relevant to the invention disclosed herein; the Suzuki et al patent discloses a current suppression circuit, not a voltage suppression circuit in accordance with the present invention, and further employs a DC/DC convertor; and the Bauman patent discloses a surge protection system for a DC power supply in which AC line voltage is filtered through an LC filter having a shunt-connected filter capacitor, and thus is not directly relevant to the circuitry provided by the invention disclosed herein. The aforementioned objects and advantages of the AC line stabilization circuitry in accordance with the present invention will now be discussed in greater detail as follows.